v1.13.0 - ask_user, cancel execution, and streaming intervention

Highlights

• Added ask_user proactive clarification via user_input_required SSE.
• Added /api/v1/agent/user-input for user input callbacks.
• Added /api/v1/agent/cancel to stop current Fixed / Auto / Flow execution.
• Improved streaming intervention UI with steer, answer_now, and cancel.
• Added V048 migration to allow ask_user in analysis steps.
• Updated README, English docs, badges, contribution guide, security notes, issue templates, and social preview image.

Verification

• mvn -pl ai-agent-station-study-trigger -am clean test-compile